This invention relates to a method of manufacturing a rotogravure printing medium and more particularly, to a method of applying a plastic printing medium to a printing roll or cylinder which is employed in rotogravure printing.
Rotogravure printing is a generally conventional method of printing on a sheet, web, or other substrate. The substrate may be a coated, uncoated, or metallized paper; glassine; plastic films and sheets made from vinyl, cellulose, acetate, polyester and polyethylene; plastic shrink films; paperboard; aluminum foil; fabrics; and similar materials. Rotogravure printing is capable of reproducing both subtle shades of color and black and white, and is particularly well suited for printing great numbers of copies precisely and rapidly. Typical end products for the printed substrates include labels, cartons, paper and plastic cups, trading stamps, wrapping paper, and sheet vinyl flooring.
Rotogravure printing is the only commercial printing process which can control both ink thickness and the area of ink coverage. This is achieved by etching or engraving recessed microscopic wells, frequently referred to as "cells," of varying depth and area in a printing medium or image carrier surface. In controlling the size and depth of the cells, the amount of ink available for placement on the substrate is controlled to generate an image composed of an arrangement of large and small dots. Other types of printing, such as flexographic printing, are generally similar to rotogravure printing, but are specifically different, e.g., as to thickness of the printing medium and the character and formation of ink-transferring surfaces.
In typical rotogravure printing, the printing medium or image carrier is a copper film electro-deposited from a chemical bath on a specially prepared steel cylinder. Prior to the engraving of the recessed wells, the copper is mechanically ground and polished. After engraving, the cylinder requires the addition of plated, hard chromium for durability and wear resistance. During the printing process the cylinder is rotated in a bath of ink. Excess ink is wiped away by a doctor blade and the ink remaining in the engraved cells is then transferred to a substrate as discrete dots, while the substrate passes between the engraved, inked cylinder and a soft pressure roller. Rotogravure printing using non-copper printing media is similarly effected.
The recommended modern process to prepare a copper image carrier requires the use of electrolytic deposition from an acid/copper bath. A steel cylinder of the required diameter is partly immersed in a chemical copper solution and rotated at a regulated speed. An electrical current running through the cylinder and the solution gradually deposits a coating of copper on the rotating cylinder until the approximate required thickness is achieved. The copper plated cylinder is washed and then polished to final dimensions with a smooth, mirror-like surface finish.
The copper coating is then engraved, either chemically or electronically. In the chemical engraving process, cells are formed by acid etching of the copper coating. The cells are formed by a screen which prevents the acid from reaching selected portions of the copper surface. The resulting acid-etched wells are round in shape and slightly smaller at the bottom than at the top.
The process of forming the copper coating for the printing cylinder and of chemically engraving the copper coating may result in the formation of waste products which are environmentally hazardous, requiring costly disposal. Further, the prior art techniques are costly and time-consuming.
An object of the present invention is a method of manufacturing a rotogravure printing medium which is inexpensive and expedient to produce and which avoids other shortcomings attending the use of copper (or other metallic) printing media.